1. Field of the Invention
The present invention relates to bridged metallocene compounds, to the corresponding ligands, to processes for preparing them and to the use of said metallocenes as components of catalysts for the polymerization of olefins.
2. Description of Related Art
Stereorigid chiral metallocene compounds possessing two bridged indenyl groups are known. They are used as components of catalysts for the polymerization of olefins, in particular for the preparation of stereo-regular polyolefins.
The numbering of the substituents on the indenyl group, to which reference is made in the present application, is as follows: 
In metallocene compounds of the type indicated above, the indenyl groups are linked together by divalent radicals that have two or more carbon atoms, such as (CH2)2 groups, or with atoms other than carbon, such as dimethylsilanediyl groups, which are generally joined to the indenyl rings in the 1 position. See, for example, European Patent Application EP-A-485 823.
European Patent Application EP-A-372 414 indicates two specific bis-indenyl metallocene compounds in which the divalent group linking the two indenyl ligands is joined in the 1 position to one indenyl ring and in the 2 position to the other indenyl ring (page 5, formulae II-1 and II-2).
International Patent Application WO 94/11406 describes a class of metallocene compounds comprising indenyl groups substituted in the 2 position. In particular, bis-indenyl compounds bridged in the 2 position on the indenyl rings are described.
New metallocene compounds have now been found which have two indenyl-type ligands linked together by a divalent group in the 4 position, and which can advantageously be used as catalyst components for the polymerization of olefins.
Therefore, in accordance with an aspect of the present invention, there are provided metallocene compounds of formula (I): 
wherein
R1 is a divalent group selected from CR42, C2R44, SiR42, Si2R44, Ger42, Ge2R44, R42SiCR42, NR4 and PR4, in which the substituents R4, which may be identical or different, are atoms of hydrogen, C1-C20 alkyl radicals, C3-C20 cycloalkyl radicals, C2-C20 alkenyl radicals, C6-C20 aryl radicals, C7-C20 alkaryl radicals or C7-C20 aralkyl radicals and can contain atoms of Si or Ge, or, when R1 is a CR42, C2R42, SiR42, Si2R44, GeR42, Ge2R44 or R42SiCR42 group, two or four substituents R4 can form one or two rings that have from 2 to 6 carbon atoms;
R2 and R3, which may be identical or different, are hydrogen atoms, C1-C20 alkyl radicals, C3-C20 cycloalkyl radicals, C2-C20 alkenyl radicals, C6-C20 aryl radicals, C7-C20 alkaryl radicals or C7-C20 aralkyl radicals and can contain atoms of Si or Ge, and in addition two substituents R2 or R3 adjacent on the same indenyl can form a ring containing from 4 to 8 carbon atoms;
M is an atom of a transition metal selected from those belonging to groups 3, 4, 5 or 6 or to the lanthanides or the actinides in the Periodic Table of the Elements (new IUPAC version);
the substituents X, which may be identical or different, are hydrogen atoms, halogen atoms, R, OR, SR, NR2 or PR2 groups, wherein the substituents R are C1-C20 alkyl radicals, C3-C20 cycloalkyl radicals, C2-C20 alkenyl radicals, C6-C20 aryl radicals, C7-C20 alkaryl radicals or C7-C20 aralkyl radicals and can contain atoms of Si or Ge.
According to another aspect of the present invention there is provided a compound of formula (II): 
and its double bond isomers, wherein R1, R2 and R3 are defined as above.
According to a further aspect of the present invention there are provided methods for the preparation of the above described compounds of formula (II).
According to a still further aspect of the present invention there is provided a catalyst for the polymerization of olefins, comprising the product of the reaction between:
(A) a metallocene compound of formula (I) as described above, and
(B) an alumoxane, or one or more compounds capable of forming an alkyl metallocene cation.
According to a still further aspect of the present invention there is provided a process for the polymerization of olefins comprising the reaction of polymerization of one or more olefinic monomers in the presence of a catalyst as described above.
The metallocene compounds according to the invention can exist in the racemic or meso isomeric form.
The divalent group R1 is preferably a C2R44 group and, more preferably, it is a (CH2)2 group.
The transition metal M is preferably selected from titanium, zirconium and hafnium, zirconium being particularly preferred.
The substituents X are preferably chlorine atoms or methyl radicals.
A particularly interesting class of metallocenes according to the invention is that of the compounds of formula (I) in which the group R1 is a (CH2)2 group, the substituents R2 in the 5 and 6 positions and the substituents R3 in the 3 positions are hydrogen atoms, the substituents R2 in the 7 positions are different from hydrogen atoms, whereas the substituents R3 in the 2 positions are preferably hydrogen atoms. Non-limiting examples of metallocene compounds belonging to the said class are:
rac- and meso-ethylenebis(7-methyl-4-indenyl)zirconium dichloride,
rac- and meso-ethylenebis(2,7-dimethyl-4-indenyl) zirconium dichloride.
Another particularly interesting class of metallocenes according to the invention is that of the compounds of formula (I) in which the group R1 is a (CH2)2 group, the substituents R2 and the substituents R3 in the 3 positions are hydrogen atoms, whereas the substituents R3 in the 2 positions are different from hydrogen atoms. Non-limiting examples of metallocene compounds belonging to the said class are:
rac- and meso-ethylenebis(2-methyl-4-indenyl)zirconium dichloride.
A third particularly interesting class of metallocenes according to the invention is that of the compounds of formula (I) in which the group R1 is a (CH2) 2 group, the substituents R2 in the 5 and 7 positions and the substituents R3 in the 3 positions are hydrogen atoms, whereas the substituents R2 in the 6 positions are different from hydrogen atoms. Non-limiting examples of metallocene compounds belonging to the said class are:
rac- and meso-ethylenebis(6-methyl-4-indenyl)zirconium dichloride,
rac- and meso-ethylenebis(6-t-butyl-4-indenyl)zirconium dichloride,
rac- and meso-ethylenebis(2,6-dimethyl-4-indenyl) zirconium dichloride,
rac- and meso-ethylenebis(2-methyl-6-t-butyl-4-indenyl) zirconium dichloride.
A forth particularly interesting class of metallocenes according to the invention is that of the compounds of formula (I) in which the group R1 is a (CH2)2 group, the substituents R2 in the 7 positions and the substituents R3 in the 3 positions are hydrogen atoms, the substituents R2 in the 5 and 6 positions form an alkylene ring, and the substituents R3 in the 2 positions are different from hydrogen atoms. Non-limiting examples of metallocene compounds belonging to the said class are:
rac- and meso-ethylenebis(2-methyl-5,6-cyclotetramethylene-4-indenyl)zirconium dichloride.
A fifth particularly interesting class of metallocenes according to the invention is that of the compounds of formula (I) in which the group R1 is a (CH2)2 group, the substituents R3 in the 3 positions are hydrogen atoms, and the substituents R2 in the 6 and 7 positions form an alkylene ring. Non-limiting examples of metallocene compounds belonging to the said class are:
rac- and meso-ethylenebis(6,7-cyclotetramethylene-4-indenyl)zirconium dichloride,
rac- and meso-ethylenebis(2-methyl-6,7-cyclotetramethylene-4-indenyl)zirconium dichloride,
rac- and meso-ethylenebis(2,5-dimethyl-6,7-cyclotetramethylene-4-indenyl)zirconium dichloride.
A sixth particularly interesting class of metallocenes according to the invention is that of the compounds of formula (I) in which the substituents R3 on each of the two cyclopentadienyl ring form an aromatic six-member ring, thus obtaining metallocene compounds bridged in the 1 position of the fluorenyl ring having the formula (Ia): 
wherein R1, R2, M and X are defined as above. Preferably the R1 group is a (CH2)2 group. These compounds are different from the known bridged bis-fluorenyl compounds in which the bridging group is linked to the fluorenyl rings in the 9 position. See e.g. European Patent Applications EP-A-524 624 and EP-A-604 908. Non-limiting examples of metallocene compounds belonging to the said class are:
rac- and meso-ethylenebis (1-fluorenyl)zirconium dichloride.
The aforementioned compounds of formula (II) are intermediate ligands that can be used for preparing the metallocene compounds of formula (I).
As in the case of the metallocene compounds of formula (I), the divalent group R1 is preferably a C2R44 group and, more preferably, it is a (CH2)2 group.
Non-limiting examples of compounds of formula (II) according to the invention are:
1,2-bis(4-indenyl)ethane,
1,2-bis(7-methyl-4-indenyl)ethane,
1,2-bis(2-methyl-4-indenyl)ethane,
1,2-bis(6-methyl-4-indenyl)ethane,
1,2-bis(6-t-butyl-4-indenyl)ethane,
1,2-bis(2,6-dimethyl-4-indenyl)ethane,
1,2-bis(2,7-dimethyl-4-indenyl)ethane,
1,2-bis(2-methyl-6-t-butyl-4-indenyl)ethane,
1,2-bis(2-methyl-5,6-cyclotetramethylene-4-indenyl)ethane,
1,2-bis(6,7-cyclotetramethylene-4-indenyl)ethane,
1,2-bis(2-methyl-6,7-cyclotetramethylene-4-indenyl)ethane,
1,2-bis(2,5-dimethyl-6,7-cyclotetramethylene-4-indenyl)ethane, and
1,2-bis(1-fluorenyl)ethane.
The compounds of formula (II) can be prepared by different methods, depending on the presence and position of substituents on the indenyl-type moieties and on the R1 group bridging them.
A particularly suitable process for preparing compounds of formula (II) in which R1 is a (CH2)2 group and at least one substituent R2 is different from a hydrogen atom, comprises the following steps:
(a) the Grignard coupling reaction of a benzyl halide of formula (III): 
wherein Y is a halogen atom, preferably a chlorine atom, and the substituents R2 have the meaning defined above, at least one substituent R2 being different from a hydrogen atom, the said reaction being carried out in the presence of metallic magnesium, preferably under reflux and in the presence of an ether solvent such as tetrahydrofuran 13(THF), diethyl ether, 1,2-dimethoxyethane or dioxane;
(b) the reaction of the 1,2-diaryl-ethane of formula (IV): 
obtained in step (a) with a compound of formula (V): 
xe2x80x83wherein Z and Zxe2x80x2 are halogen atoms, preferably chlorine atoms, and the substituents R3 have the meaning defined above, carried out in the presence of a Friedel-Crafts catalyst, such as aluminum chloride or another Lewis acid;
(c) the reaction of cyclization of the xcex2-haloacyl derivatives obtained in step (b), carried out in the presence of a strong protic acid, such as sulphuric acid;
(d) the reaction of reduction of the diketones (4,4xe2x80x2-diindanonyl-1,2-ethane) obtained in step (c), carried out in the presence of a reducing agent such as LiAlH4 or NaBH4, preferably under reflux; and
(e) the reaction of dehydration of the dialcohols obtained in step (d), carried out in an acidic environment.
Examples of compounds of formula (V) are the xcex2-halogen-propionyl halides, in particular xcex2-chloropropionyl chloride.
The benzyl halide of formula (III) and the compound of formula (V) are commercially available or can be prepared by known methods.
Depending on the position of the substituents R2 that are different from a hydrogen atom in the benzyl halide of formula (III), the reaction of cyclization of step (c) can give rise to mixtures of diketones.
In the case when, in the benzyl halide of formula (III), the substituent R2 para to the group CH2Y is different from a hydrogen atom, the various diketones that are obtained can all be converted to the desired end product. This is also true if the substituent R2 in the para position is a hydrogen atom, but the substituent R2 in the meta position is a hindering group, for example the tert-butyl group. In this case the positions a to the hindering group are inaccessible on account of the steric hindrance of the latter.
In all other cases, the desired 4,4xe2x80x2-diindanonyl-1,2-ethane diketones must be separated from the mixture of diketones that are obtained by the reaction of cyclization of step (c), for example by means of chromatographic columns.
The reactions of the other steps of the process are characterized by high yields and selectivity and therefore do not require burdensome steps of purification of the intermediates obtained.
According to one version of the said process, in step (b) the compound of formula (IV) can be reacted with a compound of formula (Vxe2x80x2): 
wherein Z, Zxe2x80x2 and the substituents R3 have the meanings defined above. In this way the cyclized product of step (c) is obtained directly. However, in this case the reaction must be conducted in controlled conditions of temperature (around xe2x88x9210xc2x0 C.) to avoid secondary reactions of polymerization, and therefore complete cyclization is not achieved.
Another interesting process for preparing compounds of formula (II), particularly suitable to prepare those in which all the R2 substituents are hydrogen atoms, comprises the following steps:
(a) the reaction of a compound of formula (VI): 
wherein R2 is defined as above and L is a leaving group such as a bromine atom a iodine atom, a tosilate or mesilate group, with a compound of formula (VII): 
xe2x80x83wherein R3 is defined as above except that it can not contain atoms of Si or Ge, and R6 is a OH, OR, NH2 or NR2 group or a halogen atom, preferably being a OH group, said reaction being carried out in the presence of a base and of a palladium(II) salt;
(b) the reaction of hydrogenation of the unsaturated compound obtained in step (a), carried out in the presence of a hydrogenation catalyst such as Raney-nickel, platinum oxide, palladium, and of a hydrogenating agent such as hydrogen or hydrazine-hydrate;
(c) the reaction of cyclization of the compound obtained in step (b), carried out in the presence of a Friedel-Crafts catalyst, such as aluminum chloride or polyphosphoric acid;
(d) the reaction of reduction of the diketones (4,4xe2x80x2-diindanonyl-1,2-ethane) obtained in step (c), carried out in the presence of a reducing agent such as LiAlH4 or NaBH4, preferably under reflux;
(e) the reaction of dehydration of the dialcohols obtained in step (d), carried out in an acidic media.
The reaction of step (a) is generally carried out in an organic solvent, such as dimethylformamide, dimethylacetamide, piridine or triethylamine, dimethylformamide being the preferred, said organic solvent being optionally in admixture with water.
The reaction of step (a), especially when the leaving groups L in the compound of formula (VI) are different from iodine atoms, can conveniently be carried out in the presence of a tri-aryl-phosphine, such as tri-o-tolyl-phosphine.
The starting compound of formula (VII), if not commercially available, can be prepared by common organic synthetic methods. In the case in which the group R1 is a (CH2)2 group, the starting compound of formula (VII) can suitably be prepared by the coupling reaction of a 2-substituted benzyl compound of formula (VIII): 
wherein R2 and L are defined as above and Yxe2x80x2 is a leaving group such as a halogen atom, a tosilate or a mesilate group, said reaction being carried out in the presence of a metal such as metallic magnesium, sodium, zinc etc., metallic magnesium being the preferred, in the presence of an organic solvent, preferably of the ether type such as tetrahydrofuran (THF), diethyl ether, 1,2-dimethoxyethane or dioxane.
A suitable way to prepare compounds of formula (II) wherein the substituents R3 in the 1 position are different from hydrogen comprises the substitution of the step (d) in the above described processes with:
(dxe2x80x2) the reaction of the diketones obtained in step (c) with organometallic compounds such as alkylmagnesium halides (Grignard reagents), alkyllithium compounds or sodium compounds.
The thus obtained compounds are then treated according to the procedure indicated under step (e) of the above described processes.
The metallocene compounds of formula (I) can be prepared by reaction of the corresponding ligands of formula (II) first with a compound capable of forming a delocalized anion on the cyclopentadienyl ring, and then with a compound of formula MZ4 wherein M is defined as above and the substituents Z are halogen atoms.
Non-limiting examples of compounds of formula MZ4 are titanium tetrachloride, zirconium tetrachloride, and hafnium tetrachloride.
In the case when at least one substituent X in the metallocene compound of formula (I) to be prepared is different from a halogen, it is necessary to substitute at least one substituent Z in the metallocene obtained with at least one substituent X different from a halogen.
The reaction of substitution of substituents Z with substituents X that are different from a halogen is carried out by methods that are in general use. For example, when the desired X substituents are alkyl groups, the metallocenes can be made to react with alkylmagnesium halides (Grignard reagents) or with alkyllithium compounds.
The metallocene compounds of the present invention can be used conveniently as catalytic components for the polymerization of olefins.
The alumoxane used in the catalyst according to the invention is considered to be a linear, branched or cyclic compound, containing at least one group of the type: 
wherein the substituents R4, which may be identical or different, are defined as for the substituents R2 or are a group xe2x80x94Oxe2x80x94Al(R4)2.
Examples of alumoxanes suitable for use according to the present invention are methylalumoxane (MAO), isobutyl-alumoxane (TIBAO) and 2,4,4-trimethylpentylaluminoxane (TIOAO). Mixtures of different alumoxanes can also be used.
Non-limiting examples of compounds capable of forming an alkyl metallocene cation are compounds of formula Y+Zxe2x88x92, wherein Y+ is a Bronsted acid capable of donating a proton and of reacting irreversibly with a substituent X of the compound of formula (I), and Zxe2x88x92 is a compatible anion which does not coordinate, which is capable of stabilizing the active catalytic species originating from the reaction of the two compounds, and which is sufficiently labile to be able to be displaced from an olefinic substrate. The Zxe2x88x92 anion preferably comprises one or more boron atoms. More preferably, the Zxe2x88x92 anion is an anion of formula BAr4(xe2x88x92), wherein the Ar substituents, which may be identical or different, are aryl radicals such as phenyl, pentafluorophenyl, bis-(trifluoromethyl)phenyl. Tetrakis-pentafluorophenyl borate is particularly preferred. Moreover, compounds of formula BAr3 can be used conveniently.
In the catalyst used in the process of the invention, both the metallocene compound of formula (I) and the alumoxane can be present as the product of reaction with an organometallic compound of aluminum of formula AlR53 or Al2R56, in which the substituents R5, which may be identical or different, are defined as for the substituents R2 or are halogen atoms.
Non-limiting examples of aluminum compounds of formula AlR53 or Al2R56 are:
Al(Me)3, Al(Et)3, AlH(Et)2, Al(iBu)3, AlH(iBu)2, Al(iHx)3, Al(C6H5)3, Al(CH2C6H5)3, Al(CH2CMe3)3, Al(CH2SiMe3)3, Al(Me)2iBu, Al(Me)2Et, AlMe(Et)2, AlMe(iBu)2, Al(Me)2iBu, Al(Me)2Cl, Al(Et)2Cl, AlEtCl2, Al2(Et)3Cl3,
wherein Me=methyl, Et=ethyl, iBu=isobutyl, iHx=isohexyl.
Of the abovementioned compounds of aluminum, trimethylaluminum (TMA) and triisobutylaluminum (TIBAL) are preferred.
The catalysts of the present invention can also be used on inert supports. This is achieved by depositing the metallocene compound (A), or the product of its reaction with component (B), or component (B) and then the metallocene compound (A), on inert supports such as silica, alumina, styrene-divinylbenzene copolymers or polyethylene.
The solid compound thus obtained, in combination with further addition of alkyl aluminum compound either untreated or pre-reacted with water, if necessary, is used advantageously in gas-phase polymerization.
In the process for the polymerization of olefins according to the invention, preferred olefinic monomers are ethylene, xcex1-olefins, such as propylene and 1-butene, cycloolefins and conjugated diolefins.
The catalysts according to the invention can be used advantageously in the reactions of homopolymerization of ethylene or of xcex1-olefins such as propylene and 1-butene, or in reactions of copolymerization of ethylene with xcex1-olefins such as propylene and 1-butene, or in reactions of copolymerization between xcex1-olefins such as propylene and 1-butene.
In particular, with the catalysts of the invention it is possible to prepare elastomeric copolymers of ethylene with xcex1-olefins of formula CH2xe2x95x90CHR, wherein R is an alkyl radical containing from 1 to 10 carbon atoms, if necessary containing minor proportions of units derived from polyenes.
The saturated elastomeric copolymers that can be obtained with the catalysts of the present invention contain from 15% to 85% in moles of ethylenic units, the complement to 100 consisting of units of one or more xcex1-olefins and/or of a nonconjugated diolefin capable of cyclopolymerizing.
The unsaturated elastomeric copolymers also contain, along with the units derived from the polymerization of ethylene and of the xcex1-olefins, minor proportions of unsaturated units derived from the copolymerization of one or more polyenes. The content of unsaturated units can vary over a wide range. Terpolymers of interest are those which contain from 0.1 to 20% by weight, preferably from 0.3 to 10% by weight, more preferably from 0.5 to 5% by weight of unsaturated units.
The elastomeric copolymers of ethylene that can be obtained with the catalysts of the invention are characterized by valuable properties, such as low ash content and uniform distribution of the comonomers in the copolymer chain.
The xcex1-olefins that can be used include, for example, propylene, 1-butene, 4-methyl-1-pentene. The preferred xcex1-olefin is propylene.
1,5-Hexadiene, 1,6-heptadiene, and 2-methyl-1.5-hexadiene can be used as non-conjugated diolefins capable of cyclopolymerizing.
The following can be used as polyenes capable of giving unsaturated units:
conjugated dienes, for example butadiene and isoprene;
nonconjugated linear dienes, for example 1,4-hexadiene trans, 1,4-hexadiene cis, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene, 11-methyl-1,10-dodecadiene;
monocyclic diolefins, for example cis-1,5-cyclooctadiene and 5-methyl-1,5-cyclooctadiene;
bicyclic diolefins, for example 4,5,8,9-tetrahydroindene and 6 and/or 7-methyl-4,5,8,9-tetrahydroindene;
alkenyl or alkylidene norbornenes, for example 5-ethylidene-2-norbornene, 5-isopropylidene-2-norbornene, exo-5-isopropenyl-2-norbornene;
polycyclic diolefins, for example dicyclopentadiene, tricyclo-[6.2.1.02.7]-4,9-undecadiene and its 4-methyl derivative.
Preferred polyenes are 5-ethylidene-2-norbornene (ENB), 1,4-hexadiene trans and 1,4-hexadiene cis, 5-ethylidene-2-norbornene being particularly preferred.
The process of polymerizing the olefins according to the invention can be carried out in the liquid phase, in the presence or absence of an inert hydrocarbon solvent, or in the gas phase. The hydrocarbon solvent can be either aromatic, such as toluene, or aliphatic, such as propane, hexane, heptane, isobutane, and cyclohexane.
The polymerization temperature is generally between xe2x88x92100xc2x0 C. and +80xc2x0 C., and more particularly between xe2x88x9250xc2x0 C. and +50xc2x0 C. The lower the polymerization temperature, the higher are the molecular weights of the polymers obtained.
The molecular weight of the polymers can, more-over, be varied by changing the type or the concentration of the catalytic components or by using molecular weight regulators, for example hydrogen.
The molecular weight distribution can be varied by using mixtures of different metallocene compounds, or by carrying out the polymerization in several steps that differ with respect to the temperatures of polymerization and/or the concentrations of molecular weight regulator.
The polymerization yields depend on the purity of the metallocene component of the catalyst. Accordingly, the metallocene compounds obtained by the process of the invention can be used as they are, or they can undergo purification treatments.
The components of the catalyst can be brought into contact with each other prior to polymerization. The duration of contact is generally between 1 and 60 minutes, preferably between 5 and 20 minutes. The precontact concentrations for the metallocene component (A) are between 10xe2x88x922 and 10xe2x88x928 mol/l, whereas for component (B) they are between 10 and 10xe2x88x923 mol/l. Precontact is generally effected in the presence of a hydrocarbon solvent and, if necessary, of small amounts of monomer.
The following examples are given by way of illustration of the invention and are non-limiting.
The ligands and metallocenes of Examples 1-3 were characterized by 1H-NMR analyses with a Bruker AC200 instrument at 200.133 MHz, using CDCl3 as solvent, at room temperature. The spectra were recorded with a 150 pulse and a relaxation delay of 1 second.
The ligands and metallocenes of Examples 14-25 were characterized by NMR analyses with a Varian Gemini 300 instrument (1H-NMR at 300 MHz, 13C-NMR at 75.4 MHz) or with a Varian XL200 instrument (1H-NMR at 200 MHz, 13C-NMR at 50.1 MHz). The solvents are as indicated and the measurements were performed at 20xc2x0 C.
13C-NMR analyses of the copolymer of Example 7 were effected with a Bruker AC200 instrument at 200.133 MHz, at a temperature of 120xc2x0 C., on samples in solution at 8% by weight in C2D2Cl4. The spectra were recorded with a 90xc2x0 pulse, a relaxation delay of 12 seconds and a number of scans of 2000-2500.
The content of ethylenic units in the ethylene/propylene elastomeric copolymers was determined by means of IR analysis, whereas the content of ethylenic units and unsaturated units in the ethylene/propylene/ENB terpolymers was determined by 1H-NMR analysis.
The polymers of Examples 26-43 were characterized by 13C-NMR analyses with a Bruker 500 instrument at 125.4 MHz. The samples were dissolved in 1,2,4-triclorobenzene with some 1,4-C6D4Cl2 added as lock. The measurements were in 5 mm NMR tobes at 130xc2x0 C. with a 70xc2x0 pulse and a relaxation delay of 15 seconds.
The intrinsic viscosity [xcex7] of the polymers of Examples 4-13 was measured in tetralin at 135xc2x0 C.
The limiting viscosity number [LVN] of the polymers of Examples 26-39 was measured at 135xc2x0 C. in decalin which was inhibited with ionol (1 g/L).
All the operations were performed in an anhydrous nitrogen atmosphere, using the conventional techniques for the handling of compounds that are sensitive to air.
MODIFIED METHYLALUMOXANE (M-MAO)
A commercial product (ALBEMARLE) was used as received, in solution (62 g Al/l) in isopar C.
TRIS-(2,4,4-TRIMETHYLPENTYL)ALUMINUM (TIOA)
This was prepared according to the method described in Liebigs Ann. Chem. Bd. 629, Ziegler et al. xe2x80x9cAluminumtrialkyls and dialkylaluminum hydrides from aluminum isobutyl compoundsxe2x80x9d pp. 14-19.